1. Field of the Invention
This invention relates to a diaphragm construction and, more particularly, diaphragm construction that embodies the structural characteristics of a short, thick beam.
Diaphragms, according to this invention, provide a higher pressure, more reliable, more durable and less costly diaphragm than previously achieved in prior art diaphragms. In a preferred embodiment, the diaphragm is constructed of a plug having a channel, tire cord reinforcement bonded to the plug and secured in the channel, an elastomer cured onto the tire cord, and a sleeve bonded to the outer circumferential surface of the elastomer.
2. Description of the Prior Art
It is known to use diaphragms in conjunction with pressurized devices, such as pumps. Exemplary of prior art diaphragms are various well-known fabric-reinforced, rubber and metal diaphragms, and seals, such as disclosed in U.S. Pat. No. 4,327,629 to Frey. Pressure and piston motion place diaphragm material under tension. All of these prior art constructions, however, are almost entirely dependent upon the tensile strength of a thin membrane to control pressure within a system.
One type of well-known diaphragm is the fabric reinforced diaphragm. The center portion of the diaphragm sits on the piston, while the outer edge of the diaphragm is clamped to the outer cylindrical housing. As the piston reciprocates, the center portion of the diaphragm is successively moved upwardly and downwardly, thereby convoluting the diaphragm, by alternatively turning it inside out and back again. The diaphragm ideally forms a flexible wall between a pumping chamber within the cylindrical housing and the piston. As the piston moves, it convolutes, and the volume of the chamber varies. With such a pump, the circumferential edge of the diaphragm near the rim of the piston experiences significant stress and is subject to tearing and other fluid leakage, permitting working fluid to flow between the piston and the cylinder and to travel to other parts beyond the piston.
Fabric-reinforced diaphragms have commonly been constructed of calendared square woven fabric cut and/or cured to a desired diameter and shape. While this particular diaphragm material has many end uses, especially in actuators, the diaphragm suffers from the constraint that it can only be used in medium to low pressure applications, commonly up to 150 psi.
Some other known diaphragms have been constructed of rubber. These diaphragms are molded rubber products that provide a thin rubber "gap". While the rubber diaphragm is low in cost, it suffers from the drawback of being able only to be operated at very low pressures.
Metal diaphragms have also been developed. These diaphragms can be used in pressures up to 35,000 psi in stages for low (metering) quantities. While these high pressures are desirable in some instances, the cost of these metal diaphragms, even for a 500-1000 psi low throughput device, is prohibitively high, commonly, around $30,000.
A well-known seal is disclosed in U.S. Pat. No. 4,327,629 to Frey. Frey discloses a seal for a cylinder piston arrangement having an elastic tube member sealingly engaging the piston and a working chamber. The tube member stretches and contracts, and the working chamber varies in volume upon relative movement of the piston and the cylinder. This seal will operate efficiently as long as the sealing tube does not experience fatigue. However, generally, the elastomer in the sealing tube will experience fatigue after a relatively small number of cycles, because the tube is under significant stress and is subject to tearing.
Diaphragms, according to this invention, can operate at sufficiently high pressures to replace the traditional piston pumps used in many hydraulic systems. In these pumps, the working fluid must be finely filtered of contaminants (on the order of 10-30 microns) and should be of a lubricating composition. The working fluid must be filtered in order to reduce the likelihood that contaminants will lodge themselves between moving elements of the device. The choice of working fluids is thus greatly limited to mainly petroleum-based liquids. Otherwise, contaminants in the working fluid could ultimately cause either the pump or the entire system to fail. In many prior art pumps, the mechanical tolerances between the piston and piston chamber are very small, in order to achieve acceptable pumping characteristics. Even if unfiltered contaminants do not cause system-wide failure, these contaminants may cause undesirable friction and wear, if they are allowed to get in between the piston and the chamber, and, thereby, reduce the efficiency of the pump. Therefore, it is very advantageous, and for most applications, necessary, to remove these contaminants.
The filtering process can also have a negative effect on the pressure realized by the device which the diaphragm is used in. Specifically, because the fluid must pass through a filter which may have entrapped contaminants therein, the flow can be impeded and the resultant pressure of the system is reduced.
In view of the above, it is apparent that the prior art diaphragms are capable of operating only at a limited range of pressures, require clean lubricating working fluid in alternate piston type hydraulic pumps, and cannot withstand the tremendous number of cycles required to meet the demands of the marketplace. Also, the cost becomes prohibitively high in order to meet the demand for a diaphragm that can operate over an extended range of pressures and at a large number of cycles. Finally, because the diaphragms are under such significant stresses and are subject to tearing and fluid leakage which permits the working fluid to flow between the piston and the cylinder, the choice of working fluids becomes unduly limited. Therefore, it would be advantageous to develop a low cost diaphragm which would substantially alleviate significant stresses on the critical elements of the diaphragm, while operating over a large range of pressures, and substantially reduce the deleterious effects which result when the working fluid leaks between the piston and the cylinder.
It is apparent, from the above, that there exists a need in the art for a diaphragm which is low cost, can be operated for a large number of cycles without developing material failure, and which can be operated over an extended range of pressures, but which, at the same time, overcomes the problems in the prior art diaphragms.